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KVM: s390: Fix lockdep issue in vm memop

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Issuing a memop on a protected vm does not make sense,
neither is the memory readable/writable, nor does it make sense to check
storage keys. This is why the ioctl will return -EINVAL when it detects
the vm to be protected. However, in order to ensure that the vm cannot
become protected during the memop, the kvm->lock would need to be taken
for the duration of the ioctl. This is also required because
kvm_s390_pv_is_protected asserts that the lock must be held.
Instead, don't try to prevent this. If user space enables secure
execution concurrently with a memop it must accecpt the possibility of
the memop failing.
Still check if the vm is currently protected, but without locking and
consider it a heuristic.

Fixes: ef11c9463ae0 ("KVM: s390: Add vm IOCTL for key checked guest absolute memory access")
Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Link: https://lore.kernel.org/r/20220322153204.2637400-1-scgl@linux.ibm.com
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
This commit is contained in:
Janis Schoetterl-Glausch 2022-03-11 18:00:40 +01:00 committed by Heiko Carstens
parent 8b202ee218
commit b5d1274409
1 changed files with 10 additions and 1 deletions
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11
arch/s390/kvm/kvm-s390.c
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@ -2384,7 +2384,16 @@ static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop)
return -EINVAL;
if (mop->size > MEM_OP_MAX_SIZE)
return -E2BIG;
if (kvm_s390_pv_is_protected(kvm))
/*
* This is technically a heuristic only, if the kvm->lock is not
* taken, it is not guaranteed that the vm is/remains non-protected.
* This is ok from a kernel perspective, wrongdoing is detected
* on the access, -EFAULT is returned and the vm may crash the
* next time it accesses the memory in question.
* There is no sane usecase to do switching and a memop on two
* different CPUs at the same time.
*/
if (kvm_s390_pv_get_handle(kvm))
return -EINVAL;
if (mop->flags & KVM_S390_MEMOP_F_SKEY_PROTECTION) {
if (access_key_invalid(mop->key))